Posts by dragosr@chaos.social
 (DIR) Post #B50OPUcQhUxyVV6Kx6 by dragosr@chaos.social
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       @azonenberg Since you've eliminated most of the signal chain, have you checked what's physically adjacent to the baseT1 fixture? Anything new or repositioned near the test setup? A switched-mode PSU, active USB hub, monitor, could be coupling into the single pair path. BaseT1 won't tolerate ambient EMI that baseTX shrugs off. Try powering down everything nearby that isn't part of the measurement and see if the eyes clean up.
       
 (DIR) Post #B50PGiYzaN1F6SsBkW by dragosr@chaos.social
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       @azonenberg AFAIR That diagonal smear pattern is characteristic of a reflection mixing with the signal (it's been a long time since I worked for a measurement equipment maker, memory fuzzy :-) ) Is there  a directional coupler to swap too? If so have you done a VNA S-sweep on it? degraded solder joint could cause reflection.
       
 (DIR) Post #B50Q2vPn6gfcrUYXsu by dragosr@chaos.social
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       @azonenberg  don't assume you have a four port VNA, but putting terminators on two and running  S21 for insertion loss (input>through), S31 for coupling factor (input>coupled), S41 for isolation (input>isolated), and S11/S22/etc. for return loss on each port individually  might show bad solder etc. with any deviations if you sweep dc->100Mhz or wider
       
 (DIR) Post #B50TZLnmpsHfpRvvO4 by dragosr@chaos.social
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       @azonenberg  i thinkkthe steel bench data is a smoking gun - environmental - 200 mV p-p just sitting on the steel bench — stronger flat, weaker elevated — confirms the bench itself is conducting or re-radiating the interference. The steel surface is coupling magnetically or capacitively to whatever the source is.38 kHz is a common switching frequency for LED drivers and small power converters. Walk around with probe and find what's radiating?It's a fox hunt.
       
 (DIR) Post #B50VEJNcqScQ90nAvo by dragosr@chaos.social
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       @azonenberg coupling:  termination > chassis ground > cable plant acting as antenna. The unpowered magjack still passes this because it's a passive magnetic coupling = no power needed.
       
 (DIR) Post #B50VwI5V0lSGsUHhmS by dragosr@chaos.social
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       @azonenberg I think wall cable acts as antenna, picks up the 38 kHz  common mode on Ethernet, passes through the magjack center taps into Bob Smith and onto media converter' ground. BaseT1 PHY TX references same ground plane for output. So when ground bounces at 38 kHz, the TX output rides with it. Modulated signal travels baseT1 link through your directional coupler into scope. The PHY being active converts ground bounce into signal-referenced noise.
       
 (DIR) Post #B5Mn93X2PiJaCFxNR2 by dragosr@chaos.social
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       Interesting critical analysis of IPv8 Draft...https://shitwolfymakes.substack.com/p/we-need-to-talk-about-the-ipv8-draft